System and method for determining start-up pressure ratio of dynamic compressor

Abstract

A controller for a system having an evaporator, a condenser, and a dynamic compressor includes a processor and a memory storing instructions that program the processor to: determine a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator; determining a first pressure at the first working fluid path based on the first heat transfer fluid temperature; determining a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser; determining a second pressure at the second working fluid path based on the second heat transfer fluid temperature; calculating a pressure ratio of the compressor according to the first pressure and the second pressure; determining a speed setpoint of the compressor based on the pressure ratio; and operating the compressor at the speed setpoint to compress the working fluid until the condition is satisfied.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. patent application No. 17 / 804,317 filed on May 27, 2022, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The field of the present disclosure relates generally to control systems and, more particularly, to control systems for dynamic compressors. Background Art

[0004] Dynamic compressors, including centrifugal compressors, are commonly used in process industries and heating, ventilation and air conditioning (HVAC) systems. The compressor is operatively connected to a motor via a shaft that supports one or more compression stages. The motor rotates the compression stages via the shaft at a selected speed and load condition to compress the refrigerant to a specified demand. The motor speed and load can be controlled to operate the compressor over a wide range of operating conditions. The operating range of the compressor is limited by a surge region at low flows and a choking region at high flows. Knowing the precise operating point of the system can help avoid operating the compressor in a surge or choking condition and minimize the duration of the compressor startup procedure.

[0005] The operating point of a dynamic compressor is determined in part by the speed of the compressor, which can be controlled by the user, and by the pressure ratio across the compressor, which is a function of the speed and load conditions of the compressor. However, it is difficult to accurately measure the pressure ratio of a dynamic compressor prior to a startup sequence because a discharge check valve downstream of the dynamic compressor prevents high pressure refrigerant from flowing from the condenser to the compressor pressure sensor to be measured. Therefore, there is a need for a system and method for determining the pressure ratio across a dynamic compressor at startup without using pressure measurements.

[0006] This section is intended to introduce the reader to various aspects of the technology that may be related to various aspects of the present disclosure, which are described and / or claimed below. It is believed that this discussion is helpful in providing the reader with background information to better understand the various aspects of the present disclosure. Therefore, it should be understood that these statements should be understood from this perspective, and not as an admission of prior art. Summary of the invention

[0007] One aspect of the present disclosure relates to a system comprising an evaporator, a condenser, and a dynamic compressor operable to compress a working fluid. The evaporator comprises a first working fluid path and a first heat transfer fluid path thermally coupled to the first working fluid path. The condenser comprises a second working fluid path and a second heat transfer fluid path thermally coupled to the second working fluid path. The dynamic compressor is fluidly coupled to the first working fluid path of the evaporator and the second working fluid path of the condenser. The system also comprises a first temperature sensor positioned within the first heat transfer fluid path of the evaporator, and a second temperature sensor positioned within the second heat transfer fluid path of the condenser. The system also comprises a controller connected to the dynamic compressor, the controller comprising a processor and a memory. The memory stores instructions for programming the processor to perform the following: receive a command to cause the compressor to begin operation; receive a first heat transfer fluid temperature from a first temperature sensor; determine a first pressure at a first working fluid path of the evaporator based on the first heat transfer fluid temperature; receive a second heat transfer fluid temperature from a second temperature sensor; determine a second pressure at a second working fluid path of the condenser based on the second heat transfer fluid temperature; determine a pressure ratio of the dynamic compressor based on the first pressure and the second pressure; determine a speed set point of the dynamic compressor based on the pressure ratio; and operate the dynamic compressor at the speed set point to compress the working fluid until a condition is met.

[0008] Another aspect of the present disclosure relates to a controller for a system, the system including an evaporator, a condenser, and a dynamic compressor fluidly connected between the evaporator and the condenser. The controller includes a processor and a memory. The memory stores instructions for programming the processor to perform the following: receiving a command to start operation of the dynamic compressor; determining a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator; determining a first pressure at a first working fluid path of the evaporator based on the first heat transfer fluid temperature; determining a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser; determining a second pressure at a second working fluid path of the condenser based on the second heat transfer fluid temperature; calculating a pressure ratio of the dynamic compressor based on the first pressure and the second pressure; determining a speed set point of the dynamic compressor based on the pressure ratio; and operating the dynamic compressor at the speed set point to compress the working fluid until a condition is met.

[0009] There are various improvements to the features associated with the above-mentioned aspects of the present disclosure. Other features may also be included in the above-mentioned aspects of the present disclosure. These improvements and additional features may exist alone or in any combination. For example, the various features discussed below with respect to any illustrated embodiment of the present disclosure may be incorporated into any of the above-mentioned aspects of the present disclosure alone or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1is a perspective view of an assembled dynamic compressor.

[0011] Figure 2 It is taken along line 2-2 Figure 1 Cross-sectional view of a dynamic compressor with the external duct removed.

[0012] Figure 3 It can be installed Figure 1 and Figure 2 Schematic diagram of an example HVAC system with a dynamic compressor shown in FIG.

[0013] Figure 4 is used for Figure 1 and Figure 2 Block diagram of the control system of the dynamic compressor shown in .

[0014] Figure 5 yes Figure 1 and Figure 2 The operation map of the dynamic compressor is shown in .

[0015] Figure 6 Yes Figure 1 and Figure 2 The method of starting pressure ratio of a dynamic compressor is shown in FIG.

[0016] Figure 7 yes Figure 1 and Figure 2 A mapping of predetermined operating points of a dynamic compressor is shown in FIG.

[0017] Fig. 8A It is used to execute Figure 1 and Figure 2 The first part of the flow chart of an example control algorithm for a startup procedure of a dynamic compressor is shown in FIG.

[0018] Figure 8B yes Fig. 8A The second part of the flowchart shown in .

[0019] Corresponding reference numerals indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

[0020] For the sake of brevity, examples will be described for a centrifugal compressor. However, the methods and systems described herein can be applied to any suitable dynamic compressor. The operation of a dynamic compressor can be improved by limiting the time that the compressor spends outside of a safe operating range during a startup procedure. The startup pressure ratio of the compressor, which represents the pressure rise between the compressor inlet and the compressor outlet, can be estimated using temperature measurements from other cycle components. The estimated pressure ratio can then be used to determine a speed set point within the safe operating range of the compressor.

[0021] Reference Figure 1 The two-stage refrigerant compressor is generally indicated at 100. The dynamic compressor 100 is operable to compress a working fluid (e.g., a refrigerant), and the dynamic compressor 100 includes a compressor housing 102, the compressor housing 102 forming at least one sealed cavity, and each stage of compression of the refrigerant is completed in the sealed cavity. The dynamic compressor 100 includes: a first refrigerant inlet 110, which is used to introduce refrigerant vapor into the first compressor stage ( Figure 1 a first refrigerant outlet 114; a refrigerant transfer conduit 112 for transferring the compressed refrigerant from the first compressor stage to the second compressor stage ( Figure 1 The refrigerant delivery conduit 112 is operatively connected to the first refrigerant outlet 114 and the second refrigerant inlet 118 at opposite ends, respectively. The second refrigerant outlet 120 delivers the compressed refrigerant from the second compressor stage to the cooling system ( Figure 3 ).

[0022] Reference Figure 2 , the compressor housing 102 encloses a first compressor stage 124 and a second compressor stage 126 located at opposite ends of the compressor 100. The first compressor stage 124 includes a first compression mechanism 106, which is configured to add kinetic energy to the refrigerant entering via the first refrigerant inlet 110. In some embodiments, the first compression mechanism 106 is an impeller. The kinetic energy imparted to the refrigerant by the first compression mechanism 106 is converted into an increased refrigerant pressure because the refrigerant velocity is slowed down when the refrigerant is transmitted to the sealed cavity (e.g., diffuser) formed in the volute 132. The first compressor stage 124 also includes a first variable inlet guide vane (VIGV) 134 disposed in the first refrigerant inlet 110 upstream of the first compression mechanism 106. The first variable inlet guide vane 134 includes a plurality of vanes, the positions of which can be controlled to introduce pre-swirl into the gaseous refrigerant entering the first refrigerant inlet 110.

[0023] Similarly, the second compressor stage 126 includes a second compression mechanism 116 configured to add kinetic energy to the refrigerant transmitted from the first compressor stage 124 and entering via the second refrigerant inlet 118. In some embodiments, the second compression mechanism 116 is an impeller. The kinetic energy imparted to the refrigerant by the second compression mechanism 116 is converted into increased refrigerant pressure because the refrigerant velocity is slowed as the refrigerant is transmitted to the sealed cavity (e.g., diffuser) formed within the volute 132. The compressed refrigerant is discharged via the second refrigerant outlet 120 ( Figure 21 (not shown) exits the second compressor stage 126. The second compressor stage 126 also includes a second variable inlet guide vane (VIGV) 136 disposed in the second refrigerant inlet 118 upstream of the second compression mechanism 116. The second variable inlet guide vane 136 includes a plurality of vanes whose positions can be controlled to introduce pre-swirl into the gaseous refrigerant entering the second refrigerant inlet 118.

[0024] The first compression mechanism 106 and the second compression mechanism 116 are connected at opposite ends of the shaft 104. The shaft 104 is operatively connected to a motor 108 positioned between the first compression mechanism 106 and the second compression mechanism 116 so that the first compression mechanism 106 and the second compression mechanism 116 rotate at a selected rotational speed to compress the refrigerant to exit the second refrigerant outlet 120 ( Figure 2 Any suitable motor including but not limited to an electric motor may be incorporated into the compressor 100.

[0025] Figure 3 It can be installed Figure 1 and Figure 2 Schematic diagram of a first example HVAC system 300 of a dynamic compressor 100. The system 300 has a single, closed refrigerant circuit including the compressor 100, a condenser 320, a first expansion device 330, and an evaporator 340. Refrigerant enters the dynamic compressor 100 at a first refrigerant inlet 110 as a low-pressure, low-temperature gas. The dynamic compressor 100 adds kinetic energy to the refrigerant and converts the kinetic energy into a pressure rise, and the refrigerant leaves the dynamic compressor 100 at a second refrigerant outlet 120 as a high-pressure, high-temperature gas. The dynamic compressor 100 may include: at least one inlet pressure sensor 111, the at least one inlet pressure sensor 111 being disposed proximate to the first refrigerant inlet 110 for measuring the refrigerant pressure upstream of the dynamic compressor 100; and at least one outlet pressure sensor 121, the at least one outlet pressure sensor 121 being disposed proximate to the second refrigerant outlet 120 for measuring the refrigerant pressure downstream of the dynamic compressor 100.

[0026] The refrigerant then enters the second working fluid path 322 of the condenser 320, which is fluidly coupled to the second compressor stage 126 downstream of the second compressor stage 126. The condenser 320 also includes a second heat transfer fluid path 324 thermally coupled to the second working fluid path 322. The second heat transfer fluid path 324 is configured to allow a heat transfer fluid to flow through the second heat transfer fluid path 324, and can form a portion of a secondary fluid loop (not shown). The heat transfer fluid can be water, ethylene glycol, refrigerant, air, or any suitable heat transfer fluid that allows the HVAC system 300 to function as described herein. The second working fluid path 322 and the second heat transfer fluid path 324 allow the condenser 320 to function as a heat exchanger, wherein the heat transfer fluid absorbs heat from the refrigerant to convert the refrigerant gas into a high-pressure, high-temperature liquid. The heat transfer fluid can then discharge heat to an external space (not shown).

[0027] The second working fluid path 322 of the condenser 320 is fluidly coupled to the first expansion device 330, which reduces the pressure of the refrigerant. In some embodiments, the pressure can be reduced until the current temperature of the liquid refrigerant becomes the boiling temperature at the pressure, and the refrigerant becomes a two-phase mixture as some of the liquid refrigerant boils and turns into a gas. The first expansion device 330 can be a fixed orifice, a thermal expansion valve, an electronic expansion valve, or any type of expansion device that allows the HVAC system 300 to function as described herein.

[0028] The first expansion device 330 is fluidly coupled to a first working fluid path 342 of the evaporator 340, which receives a low-pressure, low-temperature liquid refrigerant or a two-phase mixture of a liquid refrigerant and a gas refrigerant at its inlet. The evaporator 340 also includes a first heat transfer fluid path 344 thermally coupled to the first working fluid path 342. The first heat transfer fluid path 344 is configured to allow a heat transfer fluid to flow through the first heat transfer fluid path 344, and can form a part of a tertiary fluid loop (not shown). The heat transfer fluid can be water, ethylene glycol, a refrigerant, or any suitable heat transfer fluid that allows the HVAC system 300 to function as described herein. The first working fluid path 342 and the first heat transfer fluid path 344 allow the evaporator 340 to function as a heat exchanger. The heat transfer fluid in the first heat transfer fluid path 344 can absorb heat from the conditioned interior space or from an additional fluid loop (not shown). The refrigerant in the first working fluid path 342 absorbs heat from the first heat transfer fluid path 344 to change the phase from a liquid to a gaseous state. The first working fluid path 342 of the evaporator 340 is fluidly coupled to the first refrigerant inlet 110 upstream of the first refrigerant inlet 110 , and the cycle begins again.

[0029] The system 300 includes a first temperature sensor 360 positioned within the first heat transfer fluid path 344 of the evaporator 340. Figure 3 In the embodiment illustrated in FIG. 3 , the first temperature sensor 360 is positioned near the outlet of the first heat transfer fluid path 344 of the evaporator 340, but the first temperature sensor 360 may be positioned at any suitable location upstream, such as, but not limited to, near the inlet of the first heat transfer fluid path 344 of the evaporator 340, or within the first heat transfer fluid path 344 itself. The system 300 also includes a second temperature sensor 380 positioned within the second heat transfer fluid path 324 of the condenser 320. Figure 3 In the embodiment illustrated in FIG. 1 , the second temperature sensor 380 is positioned near the outlet of the second heat transfer fluid path 324 of the condenser 320, but the second temperature sensor 380 may be positioned at any suitable location, such as, but not limited to, near the inlet of the second heat transfer fluid path 324 of the condenser 320, or within the second heat transfer fluid path 324 itself. The first temperature sensor 360 and the second temperature sensor 380 may be thermocouples, thermistors, resistance temperature detectors (RTDs), or any other suitable type of temperature sensor.

[0030] Figure 4 An exemplary embodiment of a system 300 including a dynamic compressor 100 is shown. The compressor 100 includes: a compressor housing 102; at least one compression mechanism 106, 116; a motor 108; a speed sensor 317; pressure sensors 111, 121; and a controller 410. In the present embodiment, the dynamic compressor 100 is a two-stage centrifugal compressor, and the compression mechanism includes a first compression mechanism 106 and a second compression mechanism 116, each of which may be an impeller. In other embodiments, the dynamic compressor 100 may be an axial flow compressor, and each of the first compression mechanism 106 and the second compression mechanism 116 may be an axial flow rotor. The speed sensor 317 measures the rotational speed of the dynamic compressor 100, and the pressure sensors 111, 121 measure the pressure at the first refrigerant inlet 110 and the second refrigerant outlet 120, respectively, as shown in FIG. Figure 3 The dynamic compressor 100 may include additional pressure sensors for measuring pressure at various points along the compressor flow path. Additional sensors may be installed in the compressor 100 to provide data regarding its operation, including but not limited to temperature sensors, flow sensors, current sensors, voltage sensors, rotation rate sensors, and any other suitable sensors. The dynamic compressor 100 is not limited to the specific configuration of the system 300 and may be used with respect to Figure 1 and Figure 2The described dynamic compressor 100 is similarly configured or may be configured differently. The system 300 also includes an unloading device 301 , a variable frequency drive (VFD) 316 , and a user interface 315 .

[0031] The controller 410 is operatively connected to the dynamic compressor 100 to control its operation based at least in part on the measured parameters described above. The controller 410 includes a processor 420 and a memory 430. The memory 430 stores a map 700 of a plurality of predetermined operating points 50 of the dynamic compressor 100 (see, for example, Figure 7 ), the mapping 700 may be stored in any suitable data structure such as a table, a matrix, etc. The memory 430 also stores instructions for programming the processor 420 to determine the starting pressure ratio PR of the dynamic compressor 100. The mapping 700 of the predetermined operating point 50 and the method 600 of determining the starting pressure ratio PR of the dynamic compressor 100 will be discussed in more detail below.

[0032] The system 300 includes an interface for connecting the controller 410 to the inverter 316 and a motor interface 313 for connecting the inverter 316 to the motor 108. In some embodiments, the inverter 316 operates under the control of the controller 410. In another embodiment, the inverter 316 is a part of the controller 410. The system 300 also includes an unloading interface 314 for connecting the controller 410 to the unloading device 301.

[0033] The controller 410 is operatively coupled to the unloading device 301 via the unloading interface 314, and the unloading device 301 removes and / or reduces the load on the dynamic compressor 100 during startup and shutdown procedures, during detection of surge events, and when otherwise directed by the controller 410. In the exemplary embodiment, the unloading device 301 is a variable inlet guide vane (VIGV) ( Figure 2 ). In other embodiments, the unloading device 301 may be a variable diffuser or a bypass valve. The controller 410 is configured to control at least one operating parameter of the unloading device 301, such as the position of each variable inlet guide vane.

[0034] The system 300 also includes a user interface 315 configured to output (e.g., display) and / or receive information associated with the system 300 (e.g., information from a user). In some embodiments, the user interface 315 is configured to receive enable and / or disable input from a user to enable and disable (i.e., turn on and off) or otherwise activate operation of the system 300. Additionally, in some embodiments, the user interface 315 is configured to output information associated with one or more operating features of the system 300, including, for example, but not limited to, warning indicators such as severity alarms, occurrence alarms, fault alarms, motor speed alarms, and any other suitable information.

[0035] The user interface 315 may include any suitable input device and output device that enables the user interface 315 to function as described herein. For example, the user interface 315 may include input devices and / or other input devices including but not limited to keyboards, mice, touch screens, joysticks, throttles, buttons, switches, etc. In addition, the user interface 315 may include, for example but not limited to output devices and / or other output devices such as displays (e.g., liquid crystal displays (LCDs) or organic light emitting diodes (OLED) displays), speakers, indicator lights, instruments, etc. In addition, the user interface 315 may be a part of different components, such as a system controller (not shown). Other embodiments do not include the user interface 315.

[0036] The controller 410 is generally configured to control the operation of the dynamic compressor 100. The controller 410 controls the operation through programming and instructions from another device or controller, or is integrated with the system 300 through a system controller. In some embodiments, for example, the controller 410 receives user inputs from the user interface 315 and controls one or more components of the system 300 in response to these user inputs. For example, the controller 410 can control the motor 108 based on the user input received from the user interface 315. In some embodiments, the system 300 can be controlled by a remote control interface. For example, the system 300 may include a communication interface (not shown) configured to connect to a wireless control interface to enable remote control and activation of the system 300. The wireless control interface can be embodied on a portable computing device, such as a tablet or a smart phone.

[0037] The controller 410 may generally include any suitable computer and / or other processing unit, including any suitable combination of computers, processing units, and / or the like that may be communicatively coupled to one another and may operate independently or in association with one another (e.g., the controller 410 may form all or part of a controller network). The controller 410 may include one or more modules or devices, one or more of which may be packaged within the system 300 or may be located remotely from the system 300. The controller 410 may be part of the dynamic compressor 100 or may be independent and may be part of a system controller in an HVAC system. The controller 410 and / or components of the controller 410 may be integrated or incorporated into other components of the system 300. The controller 410 may include one or more processors 420 and associated storage devices 430 configured to perform various computer-implemented functions (e.g., perform the calculations, determinations, and functions disclosed herein).

[0038] As used herein, the term "processor" refers not only to integrated circuits, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits, and other programmable circuits. In addition, the storage device 430 of the controller 410 can generally be a storage element or include a storage element, which includes but is not limited to a computer-readable medium (e.g., a random access memory (RAM)), a computer-readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disk read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disk (DVD), and / or other suitable storage elements. Such a storage device 430 can generally be configured to store appropriate computer-readable instructions, which configure the controller 410 when executed by the processor 420 or cause the controller 410 to perform various functions described herein, including but not limited to controlling the system 300, controlling the operation of the motor 108, receiving input from the user interface 315, providing output to the operator via the user interface 315, controlling the unloading device 301, and / or various other suitable computer-implemented functions.

[0039] Reference Figure 5, an operating range or operating map 500 of an example dynamic centrifugal compressor 100 is shown. The operating map 500 graphically displays the performance of the compressor in terms of flow, head, and speed. The operating map 500 shows the percentage of the head to the value of the inlet mass flow at the design point of the dynamic compressor 100. The head is the total pressure ratio of the outlet pressure to the inlet pressure. The inlet mass flow is a measure of the amount of working fluid, such as refrigerant, flowing through the compression mechanism 106, 116. The operating map 500 shows a plurality of compressor speed lines 507. In this example, there are five speed lines 507 ranging from 70% design speed to 110% design speed, wherein the difference between each line is 10%. Although these specific speed lines are shown in this example, any number of speed lines at any different percentages of the compressor design speed can be shown for any type of compressor.

[0040] The surge limit line 504 indicates the minimum flow rate before surge occurs in the surge region 506 (i.e., to the left of the surge limit line 504). The surge control line 503 roughly indicates the minimum flow rate at which the compressor 100 can operate safely without the risk of falling into surge. The surge control line 503 is defined by a surge margin 505 relative to the surge limit line 504. By operating to the right of the surge control line 503, the dynamic compressor 100 should avoid surge. Similarly, the choke line 501 indicates that operating to the right thereof will cause the dynamic compressor 100 to operate at a choke flow rate.

[0041] The first operating point 509 of the dynamic compressor 100 is shown on the operating map 500 as the intersection of the velocity line, the inlet mass flow value, and the pressure ratio value. For example, the first operating point 509 shown in the operating map 500 is at 112% inlet mass flow, 90% head pressure, and 100% velocity, although any number of operating points may be shown for any type of compression. The operating point defines the current operating parameters of the dynamic compressor 100, and the operating map 500 indicates how close the current operating point is to operating in an unstable condition (i.e., surge) or an inefficient condition (i.e., choking).

[0042] The memory 430 stores instructions for programming the processor 420 to determine the starting pressure ratio PR of the dynamic compressor 100 . Figure 6 An example method 600 is shown in FIG. 4 . The processor 420 receives 602 a command to begin operation of the dynamic compressor 100. In some embodiments, the command may be initiated by a user, by an automatic command, or by any other suitable means. The processor 420 is also programmed to determine 604 a first heat transfer fluid temperature T at the first heat transfer fluid path 344 of the evaporator 340. 1,htf , and determining 608 a second heat transfer fluid temperature T at the second heat transfer fluid path 324 of the condenser 320 2,htfIn some embodiments, determining 604 the first heat transfer fluid temperature T 1,htf The first temperature sensor 360 receives the first heat transfer fluid temperature T 1,htf , and determining 608 the second heat transfer fluid temperature T 2,htf The second temperature sensor 380 receives the second heat transfer fluid temperature T 2,htf .

[0043] The processor 420 is also programmed to generate a temperature based on the first heat transfer fluid temperature T 1,htf Determine 606 a first pressure P at the first working fluid path 342 of the evaporator 340 1 , and based on the second heat transfer fluid temperature T 2,htf Determine 610 a second pressure P at the second working fluid path 322 of the condenser 320 2 In some embodiments, based on the first heat transfer fluid temperature T 1,htf and the second heat transfer fluid temperature T 2,htf Determine the first pressure P 1 and the second pressure P 2 Including: Based on the first heat transfer fluid temperature T 1,htf Or the second heat transfer fluid temperature T 2,htf Determine the saturation temperature T of the first working fluid 1,wf Or the second working fluid saturation temperature T 2,wf , and according to the saturation temperature T of the first working fluid 1,wf Or the second working fluid saturation temperature T 2,wf Calculate the first pressure P using the empirical equation of the working fluid 1 Or the second pressure P 2 For example, in an embodiment where the refrigerant is R134a, the saturation temperature T of the working fluid may be wf , Use the following formula to calculate the refrigerant pressure P:

[0044]

[0045] In some embodiments, the first working fluid saturation temperature T 1,wf and the second working fluid saturation temperature T 2,wf is estimated based on other system parameters. Such implementations will be discussed in more detail below.

[0046] In other embodiments, the first pressure P is determined 1 The method comprises receiving a first working fluid saturation temperature T from a data table for working fluids stored in a memory. 1,wf The corresponding first pressure value and determine the second pressure P 2 The process comprises retrieving the second working fluid saturation temperature T from the data table for the working fluid.2,wf The corresponding second pressure value. The data table may include experimental data, simulation data, or any other suitable type of data.

[0047] The processor 420 is also programmed to 1 and the second pressure P 2 Determine 612 a pressure ratio PR of the dynamic compressor 100. In some embodiments, the pressure ratio PR is determined by 2 Divide by the first pressure P 1 Calculate the estimated pressure ratio PR est To determine:

[0048]

[0049] The processor 420 is then programmed to determine 614 a speed set point N for the dynamic compressor 100 based on the pressure ratio PR. 设定点 . Reference Figure 5 , speed set point N 设定点 may be selected so that the operating point of the dynamic compressor 100 falls between the surge control line 503 and the blocking line 501 to avoid operating in unstable or inefficient conditions. For example, the processor 420 may determine the surge speed N corresponding to the pressure ratio PR 喘振 and blocking speed N 阻塞 , and determine the speed set point N 设定点 is the surge speed N 喘振 With blocking speed N 阻塞 In some embodiments, the speed set point N 设定点 It can be calculated as:

[0050] N 设定点 =N 喘振 +k·(N 阻塞 -N 喘振 )

[0051] Wherein, k is a proportionality coefficient between zero and one. In some embodiments, k may be 0.5, so that the speed set point N 设定点 Just at the surge speed N 喘振 With blocking speed N 阻塞 In other embodiments, k may be less than 0.5, so that the speed setting point N 设定点 Surge speed N 喘振 Specific blocking speed N 阻塞 In some other embodiments, k may be greater than 0.5, so that the speed set point N 设定点 Distance from blocking speed N 阻塞 Specific pitch surge speed N 喘振 Closer.

[0052] In some embodiments, the processor 420 may use the map 700 of the predetermined operating point 50 stored in the memory 430 to determine the surge speed N corresponding to the pressure ratio PR. 喘振 and blocking speed N 阻塞 .For example, Figure 7 is a representative illustration of a mapping 700 of predetermined operating points 50 stored by the memory 430. Each predetermined operating point 50 is shown as the intersection of a compressor speed value and a compressor pressure ratio value. An inlet mass flow rate is also defined for each predetermined operating point 50. The mapping 700 includes predetermined operating points 50 ranging up to and including points along the machine surge line 720 and the machine choke line 730. The mapping 700 does not include any points above the surge line 720 or below the choke line 730 because points above the surge line 720 or below the choke line 730 should be avoided and therefore these points are not "operating points". In other embodiments, predetermined operating points above the surge line 720 or below the choke line 730 may be included.

[0053] In the map 700, the range of predetermined operating points 50 is between 10% speed and 35% speed, and between 5% pressure ratio and 50% pressure ratio, where each point is 5% apart on both axes. Although these specific predetermined operating points 50 are shown in this example, any number of operating points at any value and any resolution may be shown for any type of compressor. The speed, pressure ratio, inlet mass flow rate, and variable inlet guide vane position values ​​for each predetermined operating point 50 may be generated by simulating the operation of the dynamic compressor 100 on a computer, testing the dynamic compressor 100 in a controlled environment, a combination of simulation and testing, or by any other suitable method for predetermining the speed, pressure ratio, inlet mass flow rate, and variable inlet guide vane position values ​​for each predetermined operating point 50.

[0054] The predetermined operating point 50 retrieved from the map 700 may itself indicate the choke speed or surge speed of the dynamic compressor 100 at the starting pressure ratio PR. For example, at the starting pressure ratio PR=25% head pressure, the surge speed N 喘振 is 15% of the design speed, and the blocking speed N 阻塞 is 30% of the design speed. The proportionality factor k can be selected so that the speed set point N 设定点 Falling at surge speed N 喘振 With blocking speed N 阻塞 For example, k can be selected so that the speed set point N 设定点 For 25% of the design speed, Figure 7In other embodiments, the predetermined operating point 50 retrieved from the map 700 can be used to determine the choke speed or surge speed at the starting pressure ratio PR graphically or numerically, for example, by interpolation. In other embodiments, the predetermined operating point 50 closest to the surge speed and the choke speed can be retrieved.

[0055] The processor 420 is also programmed to cause the dynamic compressor 100 to operate at a speed set point N 设定点 Operation 616 compresses the working fluid until the condition is satisfied. In some embodiments, the processor 420 causes the dynamic compressor 100 to operate at a speed set point N 设定点 Operation 616, until the predetermined start-up time has passed. The predetermined start-up time may be, for example but not limited to, 1 minute, 2 minutes, or any other suitable duration. In other embodiments, processor 420 is further programmed to determine a measured pressure ratio PR of dynamic compressor 100 meas , and the dynamic compressor 100 is set at a speed set point N 设定点 Operate until the pressure ratio PR is measured meas Exceeding the estimated pressure ratio PR est .

[0056] Measuring pressure ratio PR meas The measured pressure values ​​may be used to calculate. For example, the memory 430 may store instructions for programming the processor 420 to receive a first measured pressure P of the working fluid upstream of the dynamic compressor 100. 1,meas The first measured pressure P 1,meas It can be obtained from the inlet pressure sensor 111 disposed near the first refrigerant inlet 110. Similarly, the memory 430 can store the following additional instructions: the additional instructions program the processor 420 to receive the second measured pressure P of the working fluid downstream of the dynamic compressor 100 2,meas The second measured pressure P 2,meas The pressure can be obtained from an outlet pressure sensor 121 disposed near the second refrigerant outlet 120 .

[0057] In such an embodiment, the memory 430 stores other instructions that program the processor 420 to perform a 1,meas and the second measured pressure P 2,meas Determine the measured pressure ratio PR meas .Measurement pressure ratio PR meas The second measured pressure P can be calculated as 2,meas Divide by the first pressure P 1,meas :

[0058]

[0059] In other embodiments, the processor 420 is programmed to cause the dynamic compressor 100 to rotate at a speed set point N 设定点 Operation 616 compresses the working fluid until the pressure ratio PR is measured. meas The estimated pressure ratio PR is exceeded for the first time est Or until the scheduled start time has passed.

[0060] Fig. 8A and Figure 8B (collectively, FIG. 8 ) shows an example control algorithm 800 for calculating a start-up pressure ratio PR of a dynamic compressor according to method 600. After receiving 802 a command to start operation of the dynamic compressor 100, the processor 420 calculates 804 a first working fluid saturation temperature T at the first working fluid path 342 of the evaporator 340. 1,wf In the illustrated embodiment, the first working fluid saturation temperature T at the first working fluid path 342 is 1,wf is calculated as the first heat transfer fluid temperature T measured at the first heat transfer fluid path 344 1,wf With the first temperature offset T e The difference between .

[0061] T 1，wf =T 1，htf -T e

[0062] The first temperature offset T e The temperature difference between the saturated refrigerant in the first working fluid path 342 and the heat transfer fluid exiting the first heat transfer fluid path 344 is taken into account. The first temperature offset T e This may be, for example, but not limited to, 5 degrees Fahrenheit, 10 degrees Fahrenheit, or any other suitable temperature offset.

[0063] Similarly, in order to take into account the temperature difference between the saturated refrigerant in the second working fluid path 322 and the heat transfer fluid leaving the second heat transfer fluid path 324, a temperature offset may also be added to the second heat transfer fluid temperature T measured at the second heat transfer fluid path 324 of the condenser 320. 2,htf In the example control algorithm 800 shown in FIG. 8 , the processor 420 determines 806 what type of heat transfer fluid is used in the second heat transfer fluid path 324 of the condenser 320 and accordingly calculates 808 , 810 the second working fluid saturation temperature T at the second working fluid path 322 . 2,wf If the processor 420 determines that the heat transfer fluid is water, the second working fluid saturation temperature T at the second working fluid path 322 is 2,wf The second heat transfer fluid temperature T measured at the second heat transfer fluid path 324 may be calculated 808 as 2,htfWith the second temperature offset T cw sum:

[0064] T 2,wf =T 2，htf +T cw

[0065] The second temperature offset T cw The temperature offset may be, for example, but not limited to, 5 degrees Fahrenheit, 10 degrees Fahrenheit, 20 degrees Fahrenheit, or any other suitable temperature offset. If the processor 420 determines that the heat transfer fluid is air, the second working fluid saturation temperature T at the second working fluid path 322 is 2,wf The second heat transfer fluid temperature T measured at the second heat transfer fluid path 324 may be calculated 810 as 2,htf With the second temperature offset T ca sum:

[0066] T 2，wf =T 2，htf +T ca

[0067] The second predetermined temperature offset T ca This could be, for example, but not limited to, 10 degrees Fahrenheit, 20 degrees Fahrenheit, or any other suitable temperature offset.

[0068] In the example control algorithm 800 shown in FIG. 8 , the processor 420 is also programmed to be based on the first working fluid saturation temperature T 1,wf and the second working fluid saturation temperature T 2,wf Determine 812 the first pressure P 1 and the second pressure P 2 , and according to the second pressure P 2 Divide by the first pressure P 1 Calculate 814 estimated pressure ratio PR est The processor 420 then determines 816 that the dynamic compressor 100 is at the estimated pressure ratio PR est The surge speed N 喘振 and blocking speed N 阻塞 , and the speed set point N of the dynamic compressor 100 设定点 Calculate 818 as the surge speed N 喘振 With blocking speed N 阻塞 The value between .

[0069] The processor 420 is then programmed to cause the dynamic compressor 100 to rotate at the speed set point N 设定点 Start 820 and start the start timer. The start timer can measure the start time t 启动 , the start time t 启动Indicates the length of time that has passed since the dynamic compressor 100 began operating. The processor 420 determines 822 the start time t 启动 Has the startup completion time t been reached? 1 , and if so, it is also determined 824 that the startup is complete, and based on the measured pressure ratio PR meas The dynamic compressor 100 starts to operate. In the illustrated embodiment, the start-up completion time t 1 is 1 minute, but the startup completion time t 1 The time duration may be any suitable time duration, such as but not limited to 30 seconds, 90 seconds, or 2 minutes. 启动 The startup completion time t has not yet been reached 1 , the processor 420 also determines 826 an estimated pressure ratio PR est Or measure the pressure ratio PR meas The processor 420 then determines 828 the difference between the two pressure ratios PR est , PR meas The larger of the two corresponds to the surge speed N 喘振 and blocking speed N 阻塞 , and the speed set point N of the dynamic compressor 100 设定点 Recalculate 830 as surge speed N 喘振 With blocking speed N 阻塞 The processor 420 sets 832 the speed of the dynamic compressor 100 to the recalculated speed set point N 设定点 , and the processor 420 again determines 822 the start time t 启动 Has the startup completion time t been reached? 1 , and continue with the next steps above.

[0070] The technical advantages of the system described in this article are as follows: (1) Existing system instrumentation can be used to determine the safe operating range of the compressor during the dynamic compressor startup procedure; (2) Compressor reliability can be improved by limiting the time the compressor is outside the safe operating range.

[0071] As used herein, the terms "about," "substantially," and "approximately," when used in conjunction with a range of size, concentration, temperature, or other physical or chemical property or characteristic, are meant to encompass variations that may exist in the upper and / or lower limits of the range of the property or characteristic, including variations caused, for example, by rounding, measurement method, or other statistical variations.

[0072] When introducing elements of the present disclosure or embodiments of the present disclosure, the expressions "a," "an," "the," and "said" are intended to indicate that there are one or more elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. The use of terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the described items.

[0073] As various changes could be made in the above constructions and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A system comprising: an evaporator having a first working fluid path and a first heat transfer fluid path thermally coupled to the first working fluid path; a condenser having a second working fluid path and a second heat transfer fluid path thermally coupled to the second working fluid path; a dynamic compressor fluidly coupled to the first working fluid path of the evaporator and the second working fluid path of the condenser, the dynamic compressor operable to compress a working fluid; a first temperature sensor positioned within the first heat transfer fluid path of the evaporator; a second temperature sensor positioned within the second heat transfer fluid path of the condenser; a controller connected to the dynamic compressor, the controller comprising a processor and a memory storing instructions programming the processor to: receiving a command to initiate operation of the dynamic compressor; receiving a first heat transfer fluid temperature from the first temperature sensor; determining a first pressure at the first working fluid path of the evaporator based on the first heat transfer fluid temperature; receiving a second heat transfer fluid temperature from the second temperature sensor; determining a second pressure at the second working fluid path of the condenser based on the second heat transfer fluid temperature; determining a pressure ratio of the dynamic compressor based on the first pressure and the second pressure; determining a speed set point for the dynamic compressor based on the pressure ratio; as well as The dynamic compressor is operated at the speed set point to compress the working fluid until conditions are met.

2. The system according to claim 1, wherein: Operating the dynamic compressor at the speed set point until a condition is satisfied includes operating the dynamic compressor at the speed set point until a predetermined start-up time has elapsed.

3. A system according to claim 1 or claim 2, wherein: Determining the first pressure includes: determining a first working fluid saturation temperature at the first working fluid path of the evaporator based on the first heat transfer fluid temperature; and calculating the first pressure according to the saturation temperature of the first working fluid using an empirical equation for the working fluid; and Wherein, determining the second pressure comprises: determining a second working fluid saturation temperature at the second working fluid path of the condenser based on the second heat transfer fluid temperature; and The second pressure is calculated according to the second working fluid saturation temperature using the empirical equation of the working fluid.

4. The system according to claim 1 or 2, wherein: Determining the first pressure includes: determining a first working fluid saturation temperature at the first working fluid path of the evaporator based on the first heat transfer fluid temperature; and retrieving a first pressure value corresponding to a saturation temperature of the first working fluid from a data table for the working fluid stored in the memory, and Wherein, determining the second pressure comprises: determining a second working fluid saturation fluid temperature at the second working fluid path of the condenser based on the second heat transfer fluid temperature; and A second pressure value corresponding to the second working fluid saturation temperature is retrieved from the data table for the working fluid.

5. The system according to claim 1 or 2, wherein: Determining the pressure ratio includes calculating an estimated pressure ratio based on the second pressure divided by the first pressure.

6. The system according to claim 1 or 2, wherein: The pressure ratio is an estimated pressure ratio, and wherein the memory stores further instructions programming the processor to: receiving a first measured pressure value of the working fluid upstream of the dynamic compressor; receiving a second measured pressure value of the working fluid downstream of the dynamic compressor; and A measured pressure ratio is determined based on the first measured pressure and the second measured pressure.

7. The system according to claim 6, wherein: Operating the dynamic compressor at the speed set point until a condition is satisfied includes operating the dynamic compressor at the speed set point until the measured pressure ratio exceeds the estimated pressure ratio.

8. The system according to claim 6, wherein: Operating the dynamic compressor at the speed set point includes operating the dynamic compressor at the speed set point until a first occurrence of the measured pressure ratio exceeding the estimated pressure ratio or until a predetermined start-up time has elapsed.

9. The system according to any one of claims 1 to 8, wherein: Determining the speed set point of the dynamic compressor comprises: determining a surge speed corresponding to the pressure ratio; determining a choke velocity corresponding to the pressure ratio; and The speed set point is determined to be a value between the surge speed and the choke speed.

10. The system according to any one of claims 1 to 9, wherein: The dynamic compressor is a centrifugal compressor.

11. A controller for a system comprising an evaporator, a condenser, and a dynamic compressor fluidly coupled between the evaporator and the condenser, the controller comprising: processor; as well as a memory storing instructions for programming the processor to: receiving a command to initiate operation of the dynamic compressor; determining a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator; determining a first pressure at a first working fluid path of the evaporator based on the first heat transfer fluid temperature; determining a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser; determining a second pressure at a second working fluid path of the condenser based on the second heat transfer fluid temperature; calculating a pressure ratio of the dynamic compressor based on the first pressure and the second pressure; determining a speed set point for the dynamic compressor based on the pressure ratio; as well as The dynamic compressor is operated at the speed set point to compress the working fluid until the conditions are met.

12. The controller according to claim 11, wherein: Determining the first heat transfer fluid temperature includes receiving the first heat transfer fluid temperature from a first temperature sensor at the first heat transfer fluid path of the evaporator, and wherein determining the second heat transfer fluid temperature includes receiving the second heat transfer fluid temperature from a second temperature sensor at the second heat transfer fluid path of the condenser.

13. A controller according to claim 11 or claim 12, wherein: Determining the first pressure includes: determining a first working fluid saturation temperature at the first working fluid path of the evaporator based on the first heat transfer fluid temperature; and calculating the first pressure according to the saturation temperature of the first working fluid using an empirical equation for the working fluid; and Wherein, determining the second pressure comprises: determining a second working fluid saturation temperature at the second working fluid path of the condenser based on the second heat transfer fluid temperature; and The second pressure is calculated according to the second working fluid saturation temperature using the empirical equation of the working fluid.

14. The controller according to claim 13, wherein: Determining the first working fluid saturation temperature includes subtracting a first temperature offset from the first heat transfer fluid temperature, and wherein determining the second working fluid saturation temperature includes adding a second temperature offset to the second heat transfer fluid temperature.

15. The controller according to claim 11 or claim 12, wherein: Determining the first pressure includes: determining a first working fluid saturation temperature at a first working fluid path of the evaporator based on the first heat transfer fluid temperature; and receiving a first pressure value corresponding to a saturation temperature of the first working fluid from a data table for the working fluid stored in the memory, and Wherein, determining the second pressure comprises: determining a second working fluid saturation temperature at the second working fluid path of the condenser based on the second heat transfer fluid temperature; and A second pressure value corresponding to a saturation temperature of the second working fluid is received from the data table for the working fluid.

16. A controller according to any one of claims 11 to 15, wherein: Determining the pressure ratio includes calculating an estimated pressure ratio based on the second pressure divided by the first pressure.

17. A controller according to any one of claims 11 to 15, wherein: The pressure ratio is an estimated pressure ratio, and wherein the memory stores further instructions programming the processor to: receiving a first measured pressure value of the working fluid upstream of the dynamic compressor; receiving a second measured pressure value of the working fluid downstream of the dynamic compressor; and A measured pressure ratio is determined based on the first measured pressure and the second measured pressure.

18. The controller according to claim 17, wherein: Operating the dynamic compressor at a speed set point until a condition is satisfied includes operating the dynamic compressor at the speed set point until the measured pressure ratio exceeds the estimated pressure ratio.

19. The controller according to claim 17, wherein: Operating the dynamic compressor at the speed set point includes operating the dynamic compressor at the speed set point until the measured pressure ratio exceeds the estimated pressure ratio or until a predetermined start-up time has elapsed, which first occurs.

20. A controller according to any one of claims 11 to 19, wherein: Determining the speed set point of the dynamic compressor comprises: determining a surge speed corresponding to the pressure ratio; determining a choke velocity corresponding to the pressure ratio; and The speed set point is determined to be a value between the surge speed and the choke speed.

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